1. Technical Field
The present invention relates to an apparatus for controlling the operation of an internal combustion engine (simply engine) mounted on a vehicle that has a function for stopping idling operations thereof.
2. Related Art
In recent years, for vehicles, there have been higher requests for giving consideration to environmental issues and saving fuel consumption. One of countermeasures for those issues is to have vehicles equipped with idle stop functions (or idling stop functions). This system automatically stops the engine when the vehicle stops and automatically restarts the engine when the driver performs a given operation for restarting the running.
For making the idle stop function effective, it is general that this type of vehicle is provided with an ECU (electronic control unit) for controlling the idle stop function, besides an engine ECU (electronic control unit) for controlling the internal combustion engine (simply referred to as engines). The ECU for controlling the idle stop function is called “economic running (eco-run) ECU”. The eco-run ECU detects the state where a predetermined engine stop condition showing a vehicle stop is realized. In response to this detection, the eco-run ECU issues a request to stop the engine toward the engine ECU, and then is involved in detecting a predetermined driver's operation intended to restart the run. At the time when such a driver's operation is detected, the eco-run ECU makes the starter operate to crank the engine.
Meanwhile, when receiving the engine stop request from the eco-run ECU, the engine ECU stops the engine by stopping the supply of the fuel to the engine. And, in response to the engine cranking operation ordered by the eco-run ECU, the engine ECU will restart the engine control (such as control operations for fuel injection and ignition) for the engine restart.
Additionally, the engine ECU is equipped with a crank counter that indicates rotational positions of the crankshaft of the engine (hereinafter called a crank position). If the engine ECU has no information showing a current crank position, the engine ECU detects the current crank position on the basis of a signal coming from a crank sensor (or a cam sensor), which is outputted depending on the rotation of the crankshaft. When the current crank position is completed, the engine ECU sets to its crank counter a value corresponding to the detected current crank position. Afterward, in the engine ECU, the count of the crank counter is updated in response to the signal from the crank sensor to monitor the newest crank position continuously. Thus the engine ECU uses the information indicating the newest crank position to control the fuel injection and the ignition thereof, as can be seen in vehicles with no idle stop function.
It is significant to have a higher start performance when the engine is required to restart from its idle stop state. This start performance is evaluated on how a period of time from a driver's operation for restarting the run to the actual start of the engine. To improve this start performance, that is, to shorten such a period of time, it is necessary to continuously hold the count of the crank counter gained when the engine is stopped, even during the idle stop, without resetting the count. This operation for continuously holding the count makes it possible to start the fuel injection and ignition as early as possible at the time of restarting the engine. This is because the count of the crank counter shows the actual crank position whenever it is necessary to restart the engine, without performing again a relatively time-consuming process for detecting the crank position (that is, a process for determining cylinders).
In this situation, there has been known a technique provided by Japanese Patent Laid-open Publication No. 2000-205026. This technique relates to how to determine malfunctions relating to a rotation angle signal. Specifically, in this publication, when, of the rotation angle signal and a reference signal which are outputted depending on the rotation of the output shaft of an engine, only the rotation angle signal is outputted but no reference signal is outputted, it is determined that the rotation angle signal is malfunctioning.
As stated, the count of the crank counter is required to be held as it is during the idle stop. Thus, it is requested that the engine ECU of a vehicle having the idle stop function hold the count during the idle stop. However, this gives rise to some drawbacks, which will now be described using FIG. 10.
It is generally understood that the count of the crack counter is updated every time when the signal outputted from the crank sensor (hereinafter referred to as a crank signal) is made effective.
In addition, as shown in FIG. 10, the crank sensor has a crank rotor 2 equipped with a plurality of protrusions (which are called teeth) 1 and a pickup 3 provided so as to face the crank rotor 2. The crank rotor 2 rotates together with the crankshaft of an engine, so that the pickup 3 outputs a pulse signal every time each of the protrusions 1 passes by the pickup 3. The protrusions 1 on the crank rotors 2 have vacancies by a predetermined number of protrusions, which produce a tooth-chipped portion 4. In this kind of crank sensor, a train of pulse signals outputted from the pickup 3 is treated as an output signal from the sensor (i.e., crank signal).
In the example shown in FIG. 10, the edges of the protrusions 1 which produce effective edges of the crank signal will now be referred to as “effective edge portions.” It is possible that the engine is stopped at a timing when the effective edge portion of any protrusion 1 comes close to the pickup 3 and the crank shaft slightly reciprocates due to vibration of the vehicle and operations of on-vehicle auxiliary devices, as shown by a bidirectional arrow in FIG. 10. In this case, the engine is not in operation so that there no cranking, but noise occurs which involves the effective edges of the crank signal if the slight motions of the crankshaft are relatively large. Hence, in this case, the count of the crank counter in the engine ECU results in being updated erroneously. After this, when the engine is restarted, the engine ECU is to perform the fuel injection and ignition on the basis of the erroneous crank position, thus lowering the re-starting performance of the engine.
This problem may occur in the same way when factors other than the slight reciprocating motions of the crankshaft give noise to the crank signal. However, the technique provided by the above known publication cannot provide this kind of problem with a solution.